Nowadays, many electrical appliances are widely used with computers due to the amazing power of computers. For example, video compact disks (VCDs) and digital versatile disks (DVDs) are able to be played by a personal computer. Since the size of a typical computer monitor is not large enough to exhibit the spectacular video effect of the VCD or DVD disks, it is preferred that the signals be outputted from the personal computer to a TV set to be displayed on the relatively large TV screen. The purpose can be achieved by employing a display adapter.
FIG. 1A is a partial functional block diagram of a typical display adapter. The pixel parallel digital signals from a graphic chip 10 are selectively converted into a proper format of analog signals via either a random access memory digital-to-analog converter (RAM DAC) 11 or a TV encoder 12, and delivered to a computer monitor 13 or a TV screen 14, respectively, for display. Further, for TV analog signals, two formats, i.e. the NTSC (National Television Standards Committee) standard and the PAL (Phase Alternate Line) standard, are involved.
The functional block diagram of the TV encoder 12 can be seen in FIG. 1B. The pixel parallel digital signals from the graphic chip 10 is processed by a data capture device 121, a color space converter 122, a scaler and deflicker 123, an NTSC/PAL encoder 124 and a digital-to-analog converter 125 to produce the TV analog signals either in the NTSC, or PAL standard.
The functional block diagram of a conventional scaler and deflicker 123 can be seen in FIG. 1C. In the NTSC standard and the PAL standard, the numbers of horizontal scan lines are 525 and 625 per frame, respectively, either of which is different from that in the computer monitor standard, e.g. 600 per frame or 768 per frame. Thus, the image data outputted from the color space converter 122 needs to be scaled to be of a proper number of horizontal scan lines by a scaler 1231. The scaling step is usually proceeded by a bilinear algorithm. For example, when five scan lines are scaled into four scan lines, the color space values of the resulting second scanline correlates to those of the original second and third scan lines. Likewise, the color space values of the resulting third scan line correlates to those of the original third and fourth scan lines. For easily understanding the bilinear algorithm operation, each scanning line mentioned in the above is represented by a pixel, and the conversion is illustrated as shown in FIG. 2A. The color space values of the resulting pixel P41 is equal to that of the original pixel P51. The color space values of the resulting pixels P42 , P43 and P44 are obtained by the operations of 3(P52)/4+1(P53)/4, 2(P53)/4+2(P54)/4 and 1(P54)/4+3(P55)/4, respectively, in which (P52), (P53), (P54) and (P55) are respective color space values of the original pixels P52, P53, P54 and P55.
Along with the increasing number of horizontal scan lines in each computer monitor frame, for example up to 768, 864, 1024 or even 1200 scan lines, the scaler 1231 needs to proceed a quite large vertical reduction rate. When the scaling factor is down to a value smaller than about 0.7, the problem of losing lines could occur. That is, some horizontal scan lines will not be referred by any of the re-defined scan lines, or the re-defined image data will not incorporate therein the data of the lost line. As shown in FIG. 2B, the pixel P12 indicates a lost line that is referred by neither the pixel P22 nor the pixel P21. Thus, the color data of P12 will lose because of the scaling, resulting in a poor image quality. Likewise, this problem happens when the scaler 1231 processes horizontal scaling.
Therefore, the purpose of the present invention is to develop a method and a device for processing a non-interlacing computer image data into an interlacing TV image data to deal with the above situations encountered in the prior art.